Re: [PATCH] KVM: arm64: Unregister HYP sections from kmemleak in protected mode

[Marc Zyngier <maz@kernel.org>]

On Thu, 29 Jul 2021 17:42:15 +0100,
Catalin Marinas <catalin.marinas@arm.com> wrote:
> 
> On Thu, Jul 29, 2021 at 02:50:16PM +0100, Marc Zyngier wrote:
> > Booting a KVM host in protected mode with kmemleak quickly results
> > in a pretty bad crash, as kmemleak doesn't know that the HYP sections
> > have been taken away.
> > 
> > Make the unregistration from kmemleak part of marking the sections
> > as HYP-private. The rest of the HYP-specific data is obtained via
> > the page allocator, which is not subjected to kmemleak.
> > 
> > Fixes: 90134ac9cabb ("KVM: arm64: Protect the .hyp sections from the host")
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Cc: Quentin Perret <qperret@google.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: stable@vger.kernel.org # 5.13
> > ---
> >  arch/arm64/kvm/arm.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> > index e9a2b8f27792..23f12e602878 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -15,6 +15,7 @@
> >  #include <linux/fs.h>
> >  #include <linux/mman.h>
> >  #include <linux/sched.h>
> > +#include <linux/kmemleak.h>
> >  #include <linux/kvm.h>
> >  #include <linux/kvm_irqfd.h>
> >  #include <linux/irqbypass.h>
> > @@ -1960,8 +1961,12 @@ static inline int pkvm_mark_hyp(phys_addr_t start, phys_addr_t end)
> >  }
> >  
> >  #define pkvm_mark_hyp_section(__section)		\
> > +({							\
> > +	u64 sz = __section##_end - __section##_start;	\
> > +	kmemleak_free_part(__section##_start, sz);	\
> >  	pkvm_mark_hyp(__pa_symbol(__section##_start),	\
> > -			__pa_symbol(__section##_end))
> > +		      __pa_symbol(__section##_end));	\
> > +})
> 
> Using kmemleak_free_part() is fine in principle as this is not a slab
> object. However, the above would call the function even for ranges that
> are not tracked at all by kmemleak (text, idmap). Luckily Kmemleak won't
> complain, unless you #define DEBUG in the file (initially I tried to
> warn all the time but I couldn't fix all the callbacks).

Yeah, I had a look last week, and this fires everywhere (KVM only adds
a drop in an ocean of warnings).

> If it was just the BSS, I would move the kmemleak_free_part() call to
> finalize_hyp_mode() but there's the __hyp_rodata section as well.
> 
> I think we have some inconsistency with .hyp.rodata which falls under
> _sdata.._edata while the kernel's own .rodata goes immediately after
> _etext. Should we move __hyp_rodata outside _sdata.._edata as well? It
> would benefit from the RO NX marking (probably more useful without the
> protected mode). If this works, we'd only need to call kmemleak once for
> the BSS.

That's a good idea, and pretty easy to implement. I'll post a respin
shortly.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel